The invention relates to a power supply unit that supplies a load with electric power, and to an image forming apparatus that includes the power supply unit.
An image forming apparatus transfers a toner image formed on a photosensitive drum onto a recording medium and fixes the transferred toner image to the recording medium in a fixing section. The fixing section is provided with a heater, and applies heat and pressure to the recording medium and thereby fixes the toner image to the recording medium. To control a temperature of the heater, an effective value of an alternating-current signal to be supplied thereto may be controlled. In general, a phase control or a frequency control may be performed to control the effective value of the alternating-current signal. For example, Japanese Unexamined Patent Application Publication No. 2013-235107 discloses an image forming apparatus that performs the phase control with use of a triac upon supplying a heater with an alternating-current signal supplied from a commercial power supply.